The Queensboro Bridge spans the East River and Roosevelt Island, which used to house a number of public institutions, including a prison.

The Queensboro Bridge is a 3,725-foot (1,135 m) long five-span, two-level cantilever bridge that connects Midtown Manhattan and Long Island City in Queens. Three of the truss spans are over land, one 984-foot (300 m) long span crosses the east channel of the East River, and the other 1,182-foot (360 m) long span crosses the west channel of the East River, the latter of which was the longest cantilever span in North America until it was exceeded by the Quebec Bridge in 1917.

Locally known as the 59th Street Bridge (the title of Simon and Garfunkel's "Feelin' Groovy" song) and the Queensboro Bridge, the structure's cantilever spans are unique in that they have no suspended spans between the cantilever arms and are "through-cantilever" trusses. For this reason, some people mistakenly think that the Queensboro Bridge is a suspension bridge, particularly from the appearance of the upper chords of the eye bar chains in the long cantilever arms across the East River channels – because their overall shape resembles a catenary curve.

Plans to construct a bridge across this section of the East River—using Blackwell's Island (renamed as Welfare Island in 1921 and Roosevelt Island in 1973) as a stepping stone—were discussed as early as 1804 with a plan by Benjamin Henry Latrobe. One design by John Roebling in 1847 called for two narrow suspension spans joined by a cantilever bridge in the middle, predating his proposal for the Brooklyn Bridge. Subsequent plans in the 1880s and 1890s called for a railroad connection between Long Island and Grand Central Station (before tunnels and Pennsylvania Station were completed in 1910 and the East Side Access project was started with the construction of the 63rd Street Tunnel in 1969). A major goal of the bridge was to open up farmland in Queens for new residential development to support Manhattan's growing workforce.

The Queensboro Bridge was designed by preeminent bridge engineer Gustav Lindenthal, although other leading engineers were involved in the early planning stages, including Richard S. Buck and Othniel Foster Nichols. The bridge was originally designed as a pure cantilever span. Lindenthal changed it to a through-cantilever truss without a suspended span using massive steel eye bars for the top chord. As a continuous span under live load, its design required a computational method unique for the time. Gustav Lindenthal also reduced the width of the bridge from 120 feet (37 m) to 80 feet (24 m), adding a second deck while keeping the same carrying capacity. A panel of engineers was named to review Lindenthal's design and concluded Buck's deck plan was preferred, but also suggested a revised plan which was accepted. The plans were revised and approved in August of 1903.

The pedestrian/bicycle path on the north side of the Queensboro Bridge was used by trolleys up until 1957.

In addition to changing the design of the cantilever structure, Lindenthal commissioned architect Henry Hornbostel to add artistic details to the bridge. These included domed masonry towers on the anchorages and ornamental finials capping the bridge's towers. Decorative spires originally topped the finials and rose to a height of 406 feet (124 m) above the river, but were removed in 1960 after an inspection revealed that the steel framework supporting them had severely corroded. The spires were used as flagpoles until the 1940s; each day it would take workers several hours to climb the stairs in the towers to raise and lower the flags.

Guastavino tile vaults were used to decorate the ceiling of the cathedral-like space below the Manhattan approach of the 59th Street Bridge. First used as an open air farmers market from 1914 until 1930, the area designed by Raphael Guastavino was largely forgotten when it was later used by the Highways Department as a garage, sign shop, and storage area. After decades of extensive planning and restoration work, the 98,000-square foot (9,100 square meter) vaulted interior space east of First Avenue reopened as the "Bridgemarket" in 1999 and now includes a restaurant, supermarket, and home furnishing store.

Along with the Quebec Bridge in Canada and the Firth of Forth Bridge in Scotland, the Queensboro Bridge was considered to be one of the great three cantilever bridges in the world and had the largest carrying capacity among these structures. Nickel steel eye-bars were used for the first time in the bridge's construction, an idea of Lindenthal. They were fabricated with high grade carbon steel with nickel added to give ductility; the nickel steel eye-bars were used for tension members and ordinary structural steel was used for the compression members and floor beams. A total of 86 million pounds (39 million kg) of steel were used in the bridge's construction, which included 9 million pounds (4.1 million kg) of nickel alloy steel.

After the collapse of the Quebec Bridge during its construction in 1907, another panel of engineers was called in to review the design. The Queensboro Bridge was found to be safe, although they concluded that the structure was under designed and would not be able to accommodate four tracks for elevated railroads as originally intended. Two of these tracks were removed from the design and later built in a parallel tunnel under the East River along to accommodate BRT subway trains. The 60th Street Tunnel opened on August 1, 1920.

While under construction, the bridge was officially known as the Blackwell's Island Bridge (after a former name of Roosevelt Island, which it passes over). Just before the bridge opened, a petition was made to make the official name the Queensboro Bridge. Property owners and civic organizations in Manhattan and Queens objected the original name because of the connotation with the penitentiary, almshouse, workhouse, and other public institutions on Blackwell's Island.

The portion of the 59th Street Bridge between Manhattan and Roosevelt Island was the longest cantilever span in North America until 1917.

The Queensboro Bridge opened to vehicles and pedestrians on March 30, 1909. The lower deck carried a roadway for vehicles and two tracks for trolleys on the outside. Pedestrian promenades ran across both sides of the bridge's upper level, affording unobstructed views of the East River and its shorelines. The center of the upper level was reserved for two tracks for elevated trains. Trolleys began running across the bridge in February 1910 and continued until April 1957. The subway tracks across the bridge connected with the Second Avenue elevated line. In its early years the bridge carried two elevated railway rapid transit tracks and up to four trolley tracks. Today the bridge carries nine lanes for vehicular traffic and one pedestrian/bicycle path.

The Queensboro Bridge was designated as a National Historic Civil Engineering Landmark by ASCE in 2009, the year of its centennial anniversary. A bronze plaque is located on the south side of the bridge along East 60th Street, just west of First Avenue. The bridge was also designated as a New York City Landmark in 1974. The bridge was renamed to honor former New York City Mayor Ed Koch in April 2011.